Blade for electrophotographic apparatus

ABSTRACT

AS blade of an electrophotographic apparatus using a toner which can be integrally molded with a metallic holder and has high dimensional precision, stable charging charactersitics, and excellent properties of preventing adhesion of a toner, said blade being characterized by comprising a fluorocarbon polymer composition comprising 60 to 95% by weight of a fluorocarbon polymer, 40 to 5% by weight of a positively chargeable and non-conductive inorganic filler having an average particle diameter of 5 μm or less, and 0 to 25 parts by weight, per 100 parts by weight of the total of said fluorocarbon polymer and inorganic filler, of a conductive filler having an average particle diameter of 5 μm or less.

FIELD OF THE INVENTION

This invention relates to a blade of electrophotographic apparatus usinga toner, and more particularly, a blade of an electrophotographicapparatus which is used for controlling frictional charge of a toner,controlling the amount of the toner which is supplied to a photoreceptorin a thin film, cleaning the photoreceptor through scraping, and thelike.

BACKGROUND OF THE TECHNIQUE

Conventional blades of electrophotographic apparatus (hereinafter simplyreferred to as blades) have been made of resin materials to which ametallic plate is adhered for carrying out static charge control of atoner, thinning of a toner layer electrostatically adsorbed to atoner-feeding roller, and removal of the toner remaining on aphotoreceptor after toner transfer by scraping to clean thephotoreceptor in the development zone of a dry process electrostaticcopying machine.

The resin materials which have been generally used in such blades forelectrophotographic apparatus (hereinafter simply referred to as blades)include urethane rubbers and silicone rubbers.

The blade is generally composed of resin blade 22 of a plate shape whichis adhered to metallic holder 21 of a plate shape on surface of adhesion23 as shown in FIG. 20. The conventional blade of this type has beenmanufactured by adhering resin plate 22 to metallic holder 21 andpost-finishing the portion of the resin plate 22 to be in contact with adevelopment roller or a photoreceptor by cutting or polishing.

The materials to be used for the blades of electrophotographic apparatusare required to have properties of repelling an object in contact, suchas a toner, or allowing no penetration of such an object, as well ascharging characteristics. It is also demanded that they can bemanufactured through processes requiring no post-finishing, etc.

However, urethane rubbers which have been used in the conventionalblades of electrophotographic apparatus have problems in chargingcharacteristics and toner adhesion. Silicone rubbers also have problemsin charging characteristics. Compounding of a charge depressant asdisclosed in JP-A-No. 61-173270 sometimes brings about slightimprovements, but compounding of a charge depressant gives rise toanother problem that the blade itself becomes brittle. In addition,since the silicone rubbers are heat-curable resin having a crosslinkingstructure, they essentially require post-finishing.

Post-finishing including cutting is carried out for obtainingdimensional precision of the tip of the blade. Because the dimensionalprecision of the blade tip has influences on the state of a thin tonerlayer and the like, namely great influences on image quality, thepost-finishing for obtaining a blade of desired dimensional precisionentails much labor with inefficiency and bad economy.

DISCLOSURE OF THE INVENTION

The inventors have extensively studied the above-described problems and,as a result, settled all these problems at once by using a compositioncomprising a specific resin admixed with a specific fine powder as amaterial of blades. The present invention provides a blade of extremelyhigh performance and high dimensional precision which can be obtainedthrough a simple and easy molding method.

That is, the present invention relates to a blade of anelectrophotographic apparatus using a toner which is characterized bycomprising a fluorocarbon polymer composition which comprises 60 to 95%by weight of a fluorocarbon polymer, 40 to 5% by weight of a positivelychargeable and non-conductive inorganic filler having an averageparticle diameter of 5 μm or less, and 0 to 25 parts by weight, per 100parts by weight of the total of the fluorocarbon polymer and thenon-conductive inorganic filler, of a conductive filler having anaverage particle diameter of 5 μm or less.

Fluorocarbon Polymer

The fluorocarbon polymer to be used in a blade of an electrophotographicapparatus according to the present invention can appropriately beselected from commercially available fluorocarbon polymers, such aspolyvinyl fluoride, polyvinylidene fluoride,polychlorotrifluoroethylene, ethylene-tetrafluoroethylene copolymers,ethylene-chlorotrifluoroethylene copolymers,tetrafluoroethylene-hexafluoropropylene copolymers,tetrafluoroethylene-propylene copolymers,tetrafluoroethylene-perfluoroalkylvinyl ether copolymers, vinylidenefluoride-hexafluoropropylene copolymers, vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymers, etc. Fromthe standpoint of heat resistance and charging properties, thosecontaining a large quantity of fluorine atom, such astetrafluoroethylene and hexafluoropropylene, e.g., vinylidenefluoridehexafluoropropylene copolymers, ethylene-tetrafluoro ethylenecopolymers, and tetrafluoroethylene-perfluoroalkylvinyl ethercopolymers, are preferably used. Further, thermoplastic polymers arepreferred in view of ease in molding.

These fluorocarbon polymers may be used in combinations of two or morethereof for the purpose of controlling physical properties, such asflexibility.

Non-Conductive Inorganic Filler

The non-conductive inorganic filler which can be used in this inventionincludes those having an average particle diameter of 5 μm of less,preferably 3 μm or less, from the standpoint of uniform miscibility,appearance of molded articles, and impenetrability to liquids. Thosehaving an average particle size of more than 5 μm are not favorablebecause they cause unevenness of the surface of molded articles.

The aforesaid inorganic filler should be positively chargeable. The term"positively chargeable inorganic filler" as used herein means inorganicfillers other than those showing minus values or zero microcoulomb/gram(μC/g) as measured by a blow-off method, a method for determining chargequantity of powders (cf. Oguchi, et al., Denshishashin, Vol. 16, p. 52(1977)) Of these positively chargeable inorganic fillers, those having apositive chargeability of 5 μC/g or more are preferred.

The inorganic fillers having exhibiting such positive chargeabilityinclude, for example, magnesium oxide, zinc oxide, lead oxide, aluminumoxide, iron oxide, cobalt oxide, mica, asbestos, talc, calciumcarbonate, calcium phosphate, barium sulfate and ceramics, e.g., bariumtitanate, lead titanate, silicon nitride and silicon carbide. Inparticular, zinc oxide and magnesium oxide are preferred. Theseinorganic fillers should be stable to fluorine-containing resins becausethey come to contact with the fluorocarbon polymer in high temperaturesduring molding processing.

These inorganic fillers may be used in combinations of two or morethereof for the purpose of controlling charging properties or moldingprocessability.

Conductive Filler

The conductive filler which can be used in this invention may be any ofcarbon-based fillers, e.g., carbon black, carbon fiber, graphite, etc.,metallic fillers, e.g., metallic fine powders, metallic flakes, metallicfibers, etc., and non-conductive or conductive fillers whose surface iscoated with a conductive substance, e.g., metals, as long as it has anaverage particle diameter of 5 μm or less.

Specific examples of the conductive fillers are acetylene black, oilfurnace black, thermal black, channel black, pitch type carbon fibers,PAN type carbon fibers, natural graphite, artificial graphite, copperpowders, silver powders, nickel powders, iron powders, aluminum powders,amorphous iron powders, aluminum flakes, aluminum fibers, nickel fibers,stainless steel fibers, metal coated glass beads, metal-plated carbonblack, and so on. The shape of the conductive filler is not limited andmay be a granular form, a tabular form, or a fibrous form. Those havingan average particle size exceeding 5 μm are likely to cause unevennessof the surface of molded articles which may result in reduction ofcharge imparting properties and, therefore, are unfavorable. The averageparticle size is preferably 3 μm or less, and particularly 1 μm or less,from the standpoint of uniform miscibility, appearance of moldedarticles, charge imparting properties, and impenetrability to liquids.

Preferred of them are carbon-based fillers, with carbon black being morepreferred. In particular, those having a specific surface area of 900 m²/g or more as measured from an N₂ absorption amount according to the BETmethod are preferred because of their capability of endowing thecomposition with necessary conductivity at a low compounding ratio.

As preferable kinds of carbon-based fillers, acetylene black and furnaceblack are preferred because of their low impurity contents and excellentconductivity. Among them particularly preferred are XCF (extraconductive furnace black), SCF (super conductive furnace black), CF(conductive furnace black) and SAF (super abrasion furnace black) offurnace black Examples of XCF are "Ketjenblack EC" made by Nippon E.C.,"Vulcan XC-72" made by Cabot G. L. Inc. Examples of SCF are "Vulcan SC"and "Vulcan P" made by Cabot G. L. Inc., and "Corax L" made of DegussaCo. Examples of CF are "Vulcan C" made by Cabot G. L. Inc. and"Conductex SC" made by Columbian Co. Examples of SAF are "Asahi #90"made by Asahi Carbon Co., "Diablack A" made of Mitsubishi Chemical Ind.,Ltd., and "Vulcan 9" made by Cabot G. L. Inc.

Since these conductive fillers come to contact with the fluorocarbonpolymer in high temperatures, they should be stable tofluorine-containing resins. For example, the water content of theconductive filler is preferably not more than 0.5% by weight, morepreferably not more than 0.2% by weight. With the average particlediameter and water content being suitable, different kinds of theseconductive fillers, such as carbon black and graphite or carbon fiber,may be used in combination.

Fluorocarbon Polymer Composition

The above-described fluorocarbon polymer and non-conductive inorganicfiller and, if desired, conductive filler are mixed in a specificcompounding ratio to prepare a fluorocarbon polymer composition. Thecomposition comprises 60 to 95% by weight, preferably 65 to 92% byweight, of the polymer, 40 to 5% by weight, preferably 35 to 8% byweight, of the nonconductive inorganic filler, and 0 to 25 parts byweight, preferably 2 to 20 parts by weight, per 100 parts by weight ofthe total of the polymer and nonconductive inorganic filler, of aconductive filler. If the amount of the non-conductive inorganic filleris less than 5% by weight, that is, if the amount of the polymer exceeds95% by weight, there can be enjoyed no effects on chargingcharacteristics. On the other hand, if it exceeds 40% by weight, thatis, if the polymer is less than 60% by weight, the non-conductive fillerfinds difficulty in uniformly dispersing in the fluorocarbon polymer,causing, for example, deterioration of appearance of molded articles.Addition of the conductive filler within the above-stated range furtherenhances the effects of the present invention. However, if its amountsexceeds the above-recited range, the electric characteristics of theresulting blade deviate from the ranges required for blades.

The fluorocarbon polymer composition of the present invention cancontain other additive components as long as they do not seriouslyaffect the effects of the present invention. In particular, in order tofurther improve charging characteristics of the fluorocarbon polymercomposition, compatibility of the polymer with inorganic fillers, andmolding processability (fluidity), and the like, it is possible to addnot more than 5% by weight, preferably from 0.01 to 3% by weight, ofheat-resistant oligomers, such as positively chargeable silicone oils ornegatively chargeable fluorocarbon oligomers.

The fluorocarbon polymer composition to be used in a blade of anelectrophotographic apparatus can be prepared by means of commonlyemployed mixing or kneading machines or methods, such as rolls BrabenderPlastgraphs, extruders, and so on.

In the preparation of the composition, it is necessary to sufficientlycontrol a water content of each component. A recommended water contentof each component is 0.5% by weight or less, preferably 0.2% by weightor less, more preferably 500 ppm or less. If it exceeds theabove-recited range, adverse effects may be sometimes exerted uponcharging characteristics. Cares should also be taken about the watercontent during preservation of the composition after preparation. Thewater content of the composition during preservation is preferablycontrolled to 0.5% by weight or less. For water content control,force-drying by hot-air drying or vacuum drying is sometimes required.

The blades of electrophotographic apparatus according to the presentinvention are generally used as a composite with a metallic holder. Themetallic holder to be combined is produced from a metal selected fromthose widely employed in the art, such as aluminium, iron, stainlesssteel, copper, and brass, from the viewpoint of precision, strength,cost, and the like. Aluminum, stainless steel, or plated iron is usuallyemployed.

It is preferable that the metallic holder and the resin blade areintegrally molded, but they may be used as merely adhered to each other.Integrally molded articles can be obtained by covering a projection of ametallic holder with a molten resin or filling a recess of a metallicholder with a molten resin, followed by cooling, so that the moldedarticles may have such a structure in which the metallic holder and theresin blade may be engaging with each other. By virtue of thisstructure, the resin blade can be prevented from releasing from themetallic holder, and a high level of precision of the blade can bemaintained.

Hence, in the case of integral molding, the molding method is notrestricted as long as the resulting blade has a structure in which theresin blade and the metallic holder are engaging with each other.

The structure in which the resin blade and the metallic holder areengaging includes the following embodiments.

(1) A blade for electrophotographic apparatus composed of a resin bladeand a metallic holder supporting the resin blade, which is characterizedin that the metallic holder has a projection whose tip is larger thanthe root thereof, and the resin blade is integrally molded so as toinclude said projection.

(2) A blade for electrophotographic apparatus composed of a resin bladeand a metallic holder supporting the resin blade, which is characterizedin that the metallic holder has a recess whose bottom is larger than theopening thereof, and the resin blade is integrally molded with saidmetallic holder, said recess being filled with a part of said resinblade thereby supporting the resin blade.

(3) A blade for electrophotographic apparatus composed of a resin bladeand a metallic holder supporting the resin blade, which is characterizedin that the metallic holder has perforations in the direction differentfrom the direction of release of the resin blade, and the resin blade isintegrally molded with said metallic holder, said perforations beingfilled with a part of said resin blade thereby supporting the resinblade.

(4) A blade for electrophotographic apparatus composed of a resin bladeand a metallic holder supporting the resin blade, which is characterizedin that the resin blade is integrally molded with the metallic holder insuch a manner that said metallic holder is included within said resinblade.

The processes for producing these integrally molded articles not onlyare simpler than those for adhered articles but, when performed by useof a precise mold, do not require finishing after molding and providehigh processing precision. In addition, since the integrally moldedarticles have a structure in which the resin blade portion is hardlyreleased from the metallic holder, the necessity of exchanging parts incase of release during use can be eliminated, thus offering an advantagefrom the standpoint of after-care of products using the blade as a part.The above-described structure (4) in which the resin blade material ismolded so as to include the metallic holder is particularly preferredbecause the shape of the metallic holder is of little consideration.Methods for the integral molding include extrusion molding, injectionmolding (insert molding), compression molding, and transfer molding.Injection molding is particularly preferred in view of economy anddimensional precision.

BRIEF EXPLANATION OF THE DRAWINGS

FIGS. 1, 8, 12, 19, and 20 each illustrates a perspective view or aperspective sectional view of a blade of electrophotographic apparatusaccording to the present invention. FIGS. 2 to 5 and 9 each illustratesa cross-sectional view of a blade of electrophotographic apparatusaccording to the present invention.

FIGS. 6, 7, 10, 11, and 13 to 18 each illustrates a perspectivesectional view of a metallic holder.

FIGS. 1 to 7 depict the type of a blade obtained by integral molding byuse of a metallic holder having a projection whose tip is larger thanthe root thereof. FIGS. 8 to 11 depict the type of a blade obtained byintegral molding by use of a metallic holder having a recess whosebottom is larger than the opening thereof. FIGS. 12 to 18 depict thetype of a blade obtained by integral molding by use of a metallic holderhaving perforations. FIG. 19 depicts the type of a blade obtained byintegrally molding a resin blade material so as to include a metallicholder. FIG. 20 depicts the type of a blade obtained by adhering ametallic holder and a resin blade. 1 . . . Blade of Electrophotographicapparatus 2 . . . Metallic holder 2a . . . Projection 2b . . . Recess 3. . . Resin composition 5 . . . Perforation 6 . . . Fixing portion 7 . .. Direction of release of blade 8 . . . Direction perpendicular to 7 9 .. . Recess 21 . . . Metallic holder of a plate shape 22 . . . Resinblade of a plate shape 23 . . . Surface of adhesion

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION EXAMPLES 1 TO 2 ANDCOMPARATIVE EXAMPLES 1 TO 2

Prior to carrying out the following embodiment, the resin component wasadjusted to have a bound water content of 500 ppm or less by hot-airdrying, and the non-conductive inorganic filler component was adjustedto have a water content of 500 ppm or less by vacuum drying at 120° C.

A resin component comprising 83.3% by weight of vinylidene fluoridepolymer pellets ("Kynar 720", produced by Pennwalt, Co.), 11.1% byweight of cold-ground vinylidene fluoride polymer of the same kind, and5.6% by weight of a fluorine-containing rubber ("Viton B-50, produced byE. I. Du Pont de Nemours & Co., Inc.) and a positively chargeablenon-conductive inorganic filler component comprising 20% by weight ofmagnesium oxide (average particle diameter: 1 μm) and 80% by weight ofzinc oxide (average particle diameter 0.5 μm) were dry blended at aratio shown in Table 1. The resulting dry blend was kneaded in a ventedtwin-screw extruder having a diameter of 30 mm at 245° C. to preparepellets of a resin composition.

Separately, metallic holder 2 having projection 2a as shown in FIG. 1was produced from stainless steel (SUS 304). The resin compositionpellets above prepared were injection molded onto the metallic holder 2by means of an injection molding machine ("Nissei 80T" molding machine)to obtain blade 1 of an electrophotographic apparatus having a structurein which the projection 2a of the metallic holder 2 was covered with theresin composition 3.

The resulting molded article was fitted to an electrophotographicapparatus for testing. The test was carried out by passing a tonerthrough the interface between a developing roller and the molded articlecontacted with said roller under a load of 450 g, and the state ofadhesion of the toner melted and solidified to the blade due to frictionbetween the blade and the toner was observed, and the charge quantity ofthe electrified toner was measured.

With respect to dimensional precision of the molded article, the degreeof influences of the straightness of the flat plane at the tip onformation of a thin layer of a toner was evaluated by passing a tonerthrough the interface between the developing roller and the blade tospread the toner in a thin film, transferring the thin toner film ontoan adhesive tape, and observing the unevenness of the toner density andoccurrence of white streaks. The unevenness of the toner density andwhite streaks appear on reproduced images in the same state and are thusunfavorable. The results on the test are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                 Comparative        Comparative                                                Example 1                                                                            Example 1                                                                           Example 2                                                                           Example 2                                                                            Remark                                 __________________________________________________________________________    Composition:                                                                  Total Amount of Fluoro-                                                                    97     90    65    55                                            carbon Polymer (wt  %)                                                        Total Amount of Non-                                                                       3      10    35    45     Foaming was observ-                    conductive Inorganic                   ed in the molded                       Filler (wt  %)                         article of Comp. Ex. 2.                Adhesion of Toner                                                                          not    not   not   observed                                                                             Toner adhesion in-                                  observed                                                                             observed                                                                            observed     hibits impartment of                                                          sufficient charge and                                                         formation of uniform                                                          thin toner layer.                      Charging of Toner:                                                            In using Positively                                                                        O      O     O     X      A good balance of                      Chargeable toner (μC/g)                                                                 +20    +15   +14   +3     charge quantity of                                                            toner between + and -                  In Using Negatively                                                                        X      O     O     X      is desirable.                          Chargeable Toner (μC/g)                                                                 -2     -15   -13   -3     Rating System:                                                                0 to 3 μC/g: x                                                             3 to 7 μC/g: Δ                                                       7 to 20 μC/g: O                                                            more than 20 μC/g: Δ                                                 ˜ x                              Condition of Toner Thin                                                                    Δ                                                                              O     O     X      O: uniform                             Layer                                  Δ: slight unevenness                                                    of density observed                                                           X: white streaks and                                                          unevenness of den-                                                            sity observed                          Overall Evaluation                                                                         X      O     O     X                                             __________________________________________________________________________

EXAMPLES 3 TO 4 AND COMPARATIVE EXAMPLES 3 TO 4

A vinylidene fluoride-hexafluoropropylene copolymer ("Kynar 2800",produced by Pennwalt, Co.), positively chargeable zinc oxide having anaverage particle diameter of about 0.5 μm which had been dried so as tohave a water content of 200 ppm or less, and, as a conductive filler,carbon black ("Ketjenblack EC") whose water content had been adjusted to0.5% by weight or less were dry blended at a ratio shown in Table 2. Theresulting dry blend was kneaded in a vented twin-screw extruder having adiameter of 30 mm at 245° C. to obtain pellets having an averageparticle diameter of about 3 mm.

The pellets were injection molded as an integral part of a metallicholder in the same manner as in Example 1 to obtain blade 1 of anelectrophotographic apparatus. The resulting blade was evaluated in thesame manner as in Example 1, and the results obtained are shown in Table2.

                                      TABLE 2                                     __________________________________________________________________________                  Comparative        Comparative                                                Example 3                                                                            Example 3                                                                           Example 4                                                                           Example 4                                    __________________________________________________________________________    Composition:                                                                  (a) Amount of Fluoro-                                                                       100    80    80    80                                           carbon Polymer (wt %)                                                         (b) Amount of Non-                                                                          --     20    20    20                                           conductive Inorganic                                                          Filler (wt %)                                                                 (c) Amount of Con-                                                                          --     4     20    30                                           ductive Filler (part by wt.)                                                  Adhesion of Toner                                                                           not    not   not   observed                                                   observed                                                                             observed                                                                            observed                                           Charging of Toner:                                                            In using Positively                                                                         Δ                                                                              O     O     X                                            Chargeable Toner (μC/g)                                                                  +22    +17   +17   +3                                           In using Negatively                                                                         X      O     O     X                                            Chargeable Toner (μC/g)                                                                  -1     -17   -16   -3                                           Condition of Toner Thin                                                                     Δ                                                                              O     O     X                                            Layer                                                                         Overall Evaluation                                                                          X      O     O     X                                            __________________________________________________________________________     Note:                                                                         The amounts of the components (a) and (b) are based on (a) + (b).             The amount of the components (c) is based on 100 parts by weight of (a) +     (b).                                                                     

INDUSTRIAL APPLICABILITY

The blade of electrophotographic apparatus according to the presentinvention can be produced from a material exhibiting high dispersionqualities making use of mutual actions between the fluorocarbon polymerresin and the positively chargeable inorganic filler and, if used, theconductive filler through a simple and easy process while realizing highdimensional precision, taking the full advantage of the characteristicsof thermoplasticity. The excellent dispersion qualities of the materialendow the blade with stable charging characteristics and prevent tonerfrom adhesion. Further, the material can be molded integrally with ametallic holder by a simple and easy molding method so that highfunction and high performance blades having high dimensional precisioncan be mass-produced in low cost for a merit of the process.

What is claimed is:
 1. A blade of an electrophotographic apparatus usinga toner, which is characterized in that the blade comprises afluorocarbon polymer composition comprising 60 to 95% by weight of afluorocarbon polymer, 40 to 5% by weight of a positively chargeable andnon-conductive inorganic filler having an average particle diameter of 5μm or less, and 0 to 25 parts by weight, per 100 parts by weight of thetotal of said fluorocarbon polymer and inorganic filler, of a conductivefiller having an average particle diameter of 5 μm or less.
 2. A bladeas claimed, in claim 1, wherein said fluorocarbon polymer is avinylidene fluoride-hexafluoropropylene copolymer, anethylene-tetrafluoroethylene copolymer, or atetrafluoroethylene-perfluoroalkylvinyl ether copolymer.
 3. A blade asclaimed in claim 1 or 2, wherein said positively chargeable andnon-conductive inorganic filler is zinc oxide or magnesium oxide.
 4. Ablade as claimed in claim 1 or 2, wherein said conductive filler is acarbon-based filler.
 5. A blade as claimed in claim 4, wherein saidcarbon-based filler is acetylene black or furnace black.
 6. A blade asclaimed in claim 5, wherein said furnace black is XCF (extra conductivefurnace black), SCF (super conductive furnace black), CF (conductivefurnace black), or SAF (super abrasion furnace black).
 7. A blade asclaimed in claim 1 or 2, wherein said blade is integrally molded with ametallic holder.
 8. A blade as claimed in claim 7, wherein said blade isintegrally molded with said metallic holder so as to cover a projectionof said metallic holder whose tip is larger than the root thereof.
 9. Ablade as claimed in claim 7, wherein said blade is integrally moldedwith said metallic holder, with a part of said blade being filled in arecess of said metallic holder whose bottom is larger than the openingthereof.
 10. A blade as claimed in claim 7, wherein said blade isintegrally molded with said metallic holder, with a part of said bladebeing filled in perforations provided in said metallic holder to thedirection different from the direction of release of the blade.
 11. Ablade as claimed in claim 7, wherein said blade is integrally moldedwith said metallic holder so as to include the metallic holder therein.